180 TKANSACTIONS AND PKOCKKDINGS OF THE [Hess. Lxvi. 



the view of exliibiting this interesting property in its 

 many varied aspects. 



Gravity. — When a stem laid horizontally continues to 

 grow in the same direction for some time Ijefore curving 

 geotropically it exhibits functional inertia of anabolism. 

 The time value of the inertia varies for different members, 

 fi'om a few minutes (Darwin, "Nature," vol. 65 p. 44) to 

 an hour or more (Detmer, " Physiology," p. 443). When 

 the shoot curves past the vertical — the point of zero 

 stimulation, — the other phase of katabolic inertia is pre- 

 sented. This is, to use Harris's analogy, the door swinging 

 after you have ceased to push it. In those cases where a 

 sense organ has been proved to exist (Pfeffer, " Annals of 

 Botany," viii. p. 317, and Darwin, "Annals of Botany," 

 vol. xii. p. 5G7), from which the impulse is transmitted to 

 a responsive organ, transmission time — including Czapek's 

 exposition and presentation period — has to be deducted 

 from the reaction time to obtain the time value of the 

 inertia. 



To place an upright support in the way of a twiner 

 whose movement is due in part at least, if not entirely, to 

 lateral geotropism, is a case of mechanically inhibiting a 

 movement. If the support be removed before growth has 

 rendered the curvature permanent, the revolving movement 

 recommences, but only after a latent period, varying from 

 a few hours to a few days (Darwin, " Climbing Plants," 

 p. 21). This is katabolic inertia. 



Light and darhiess. — Light acts as a stimulus in virtue 

 of its intensity and also of the direction of its incident 

 rays. A plant which has been growing rapidly during the 

 night does not have its grov/th retarded immediately on 

 the approach of daylight, nor when placed in darkness 

 after being exposed to light is its growth immediately 

 accelerated. In both cases, for an hour or more (Sach's 

 "Physiology," p. 559; Vines' "Physiology," p. 395), in 

 virtue of the functional inertia of the protoplasm, the 

 previous conditions continue, and the growth curve con- 

 tinues to rise in the first instance and to fall in the 

 second. 



When Bacterium jihofomctricum (Vines' " Physiology," 

 p. 523) is placed in darkness its movements are inhibited, 



